Ph4n70m has the right idea!
Listen to him guys & gals!
1. Select maze as map
2. Put nightmare mode on
3. Turn off devils, collisions, and friendly fire
4. Begin game
5. Quickly press previous weapon to switch to rocket launcher
6. Keep firing at the entrance from where you're stood, no need to go anywhere else
8. If you run out of rocket launcher ammo switch to shotgun while running back a bit, but easier if you just dart in and grab goodies while firing at zombies
8. Run in and pick up goodies while shooting/before the next round
9. Run in a zig-zag pattern so they can't hit you and don't stop!
10. Get a ridiculously high score in everything!
Add me yay!